Communication technologies that link electronic devices in a networked fashion are well known. Examples of communication networks include wired packet data networks, wireless packet data networks, wired telephone networks, wireless telephone networks, and satellite communication networks, among other networks. These communication networks typically include a network infrastructure that services a plurality of client devices. The Public Switched Telephone Network (PSTN) is probably the best-known communication network that has been in existence for many years. The Internet is another well-known example of a communication network that has also been in existence for a number of years. These communication networks enable client devices to communicate with each other on a global basis. Wired Local Area Networks (LANs), e.g., Ethernet, are also quite common and support communications between networked computers and other devices within a serviced area. LANs also often link serviced devices to Wide Area Networks and the Internet. Each of these networks is generally considered a “wired” network, even though some of these networks, e.g., the PSTN, may include some transmission paths that are serviced by wireless links.
One common data network architecture, specified as the Data Over Cable Service Interface Specification (DOCSIS) is a standard developed for cable data communications. The goal of DOCSIS is to define a data service that will allow transparent bi-directional transfer of Internet Protocol (IP) traffic between a cable system headend or Cable Modem Termination System (CMTS) and customer locations using a cable modem (CM), over an all-coaxial or hybrid-fiber/coax (HFC) cable network.
A DOCSIS Media Access Control (MAC) utilizes a time division multiple access (TDMA) technique to facilitate communications between cable modems and the Cable Modem Termination System (CMTS), or headend, in the upstream path (i.e. from subscriber to head-end). DOCSIS TDMA access is accomplished by assigning upstream time slots within which cable modems transmit their messages to the headend. Each timeslot granted to a modem is an integer number of minislots, which are the basic MAC timing unit for allocation and granting TDMA slots. In DOCSIS, minislot timing is derived from the MAC global time reference clock, such that each minislot begins and ends upon a rising edge of the clock.
The DOCSIS MAC sublayer specifies that the CMTS provide a single carrier transmitter for each downstream (i.e. from head-end to subscriber) channel. All CMs at subscriber locations listen to all frames transmitted on the downstream channel upon which they are registered and accept those frames where the destinations match the CM itself or CPEs (customer premises equipment). CMs can communicate with other CMs only through the CMTS.
The upstream channel is thus characterized by many transmitters (CMs) and one receiver (the CMTS). Time in the upstream channel is slotted, providing for TDMA at regulated time ticks. The CMTS provides the time reference and controls the allowed usage for each interval. Intervals may be granted for transmissions by particular CMs, or for contention by all CMs. CMs may contend to request transmission time. To a limited extent, CMs may also contend to transmit actual data. In both cases, collisions can occur and retries are then used.
The DOCSIS MAC transmits a 32 bit timestamp message derived from the 10.24 MHz global time reference at the CMTS in the downstream channel to all subscribers for the purpose of upstream transmission synchronization. Subscriber modems use this timestamp message to produce a local version of the global time reference that is synchronized to the CMTS clock.
The DOCSIS protocol has been adapted to other types of media, including terrestrial fixed wireless and two way satellite. For these applications, as well as the original data over cable service, data is transferred between a central location and many remote subscribers. Satellite communication systems include a satellite earth station, a satellite, and a plurality of satellite receivers. The satellite earth station includes a large satellite dish and servicing satellite earth station electronics. Satellite receivers include relatively smaller satellite dishes and also include servicing electronics. Historically, satellite communication systems were used for the broadcast of television and radio programming. However, satellite communication systems have also been used for servicing data communications. Early satellite communication systems delivered data downstream via the satellite receiver. However, upstream data was typically received via a different data path, e.g., dial-up modem.
Newer satellite communication systems that service data communications receive upstream data via the satellite and satellite earth station. Thus, in such systems, the customer equipment includes not only a receiver but also a transmitter. While the newer satellite communication systems have the advantage of servicing both downstream and upstream communications via the satellite communication path, the serviced data rates are slow. Thus, heretofore, satellite communication systems that service data communications have provided lesser data rates than other systems, e.g., cable modem systems, Digital Subscriber Line systems, etc.
Therefore, there is a need for an improved satellite communication system that provides adequate service for both downstream and upstream data communications.